Yeah, I mean I don't want to just say "you're wrong", but you kind of are here. TypeScript alone doesn't make any assertions and doesn't offer any checking at

Yeah, I mean I don't want to just say "you're wrong", but you kind of are here. TypeScript alone doesn't make any assertions and doesn't offer any checking at system boundaries ("external inputs"). That's not what it is for, and the types you specify with it aren't objects. All that stuff gets compiled out before the code is even run. The point of TypeScript is so that you don't have to run your code to know whether the way it handles data internally is the way you intend it to. Validation at system boundaries is a separate concern, and handled separately. I like to do it with a package called "runtypes", which both supports arbitrarily complex shapes in its validators, and expresses them in a way that's very close to TS and can be trivially converted into compile-time TS types so that you don't have to write the same types twice. I wasn't sure what to make of TypeScript for a while, too. But having once tried it, and since become very conversant with it, I'll go back only for trivial tasks or under significant duress. Sure, writing types is a fair bit more work up front and a little more ongoing, but it really does make a huge difference in maintainability; in my experience, it's a little work now to save a lot of work later, as the resulting code is both less likely to exhibit an entire class of often quite subtle bugs, and easier to reason about and modify.